1. Field of the Invention
This invention relates to conductive materials, more specifically, to undoped conductive organic ladder polymers.
2. Description of the Prior Art
Numerous resinous compositions that conduct electricity are known. Many are an organic resin with a conductive material, such as metal or graphite, dispersed in the resin. This type of conductive polymer is exemplified by Japanese patent No. 87/29007 which teaches kneading 20 parts of nickel coated wollastonite into 80 parts of polyoxymethylene. The mechanical properties for this type of conductive polymers are deficient in areas such as flexibility, moldability and durability.
Conductive polymers also can be obtained by precise pyrolytic treatment of a polymer such as a phthalonitrile resin. As disclosed in "Phthalonitrile-based Conductive Polymer"-Keller, J. of Pol. Sci., Vol. 25, p. 2569-2576 (1987), pyrolysis of a thermosetting resin resulted in a continuous network of polyconjugated fused rings which were conductive. Polymers made in this manner are stable but conductivity varies as a result of minor differences in pyrolytic temperature and annealing time.
Polymers which are complexed with a dopant such as radical anion salts of 7,7,8,8-tetracyanoquinodimethane (TCNQ) are other examples of conductive polymers. As shown in U.S. Pat. No. 3,966,987, TCNQ is added to a polymer in a mutual solvent to form a solution from which a film is cast. The resulting polymer is conductive but can be chemically and electrically unstable in ambient conditions.
In earlier studies of undoped polymeric conductors by this inventor, heteroaromatic ladder polymers were found to be stable and highly intrinsic semiconductors. These properties were mainly the result of a coplanar ladder structure. One example is phenothiazine ladder (PTL) polymer prepared by polycondensation of 2,5-diamino-1,4-benzenedithiol (DADT) and 2,5-dichloro-p-benzoquinone (U.S. Pat. No.4,618,453). A typical value for conductivity for undoped PTL polymer is 5.0.times.10.sup.-6 S/cm. Doping the PTL polymer with a protonic acid material such as ClSO.sub.3 H increases the conductivity to a typical value of 2.1.times.10.sup.-2 S/cm. It would be advantageous to have increased conductivity without doping.